Mineralization Of Phenol Research Articles

Enhanced Photocatalytic Degradation Performance by Micropore-Confined Charge Transfer in Hydrogen-Bonded Organic Framework-Like Cocrystals.

Carrier utilization in organic photocatalytic materials is unsatisfactory due to the large exciton binding energy and short exciton diffusion length. Both donor-acceptor (D-A) strategies and porous designs are promising approaches to improve carrier utilization in photocatalysts. However, a more efficient way is to shorten the distance of exciton migration to the catalyst surface by the charge transfer (CT) process. Herein, hydrogen-bonded organic framework-like cocrystal (NDI-Cor HOF-cocrystal) is prepared with novel structures serving as a proof of concept for the approach, using N, N'-bis (5-isophthalate) naphthalimide (NDI-COOH) as the porous framework and acceptor, and Coronene (Cor) as the donor unit. CT and porous engineering are integrated through cocrystal strategy. Under light irradiation, photogenerated excitons transfer and dissociate from the inner surface of the micropores on a hundred-picosecond time scale, where efficient radical transformation and further redox reactions with adsorbed phenol molecules occur. NDI-Cor HOF-cocrystal photocatalytic degradation of phenol is 15 times higher than that of original HOFs, and achieves near 90% deep mineralization of phenol. Significantly, this work has designed novel HOF-cocrystal and also provides new modification strategies for high performance organic photocatalysts.

Influence of UV-A Light Modulation on Phenol Mineralization by TiO2 Photocatalytic Process Coadjuvated with H2O2

Influence of UV-A Light Modulation on Phenol Mineralization by TiO2 Photocatalytic Process Coadjuvated with H2O2

Niche construction in a bioelectrochemical system with 3D-electrodes for efficient and thorough biodechlorination

The design of bioelectrochemical system based on the principle of niche construction, offers a prospective pathway for achieving efficient and thorough biodechlorination in groundwater. This study designed a single-chamber microbial electrolysis cell, with porous three-dimensional (3D) electrodes introduced, to accelerate the niche construction process of functional communities. This approach allowed the growth of various bacteria capable of simultaneously degrading 2,4-dichlorophenol (DCP) and its refractory intermediates, 4-chlorophenol (4CP). The 3D-electrodes provided abundant attachment sites for diverse microbes with a high initial Shannon index (3.4), and along the degradation progress, functional bacteria (Hydrogenoanaerobacterium and Rhodococcus erythropolis for DCP-degrading, Sphingobacterium hotanense for 4CP-degrading and Delftia tsuruhatensis for phenol-degrading) constructed their niches. Applying an external voltage (0.6 V) further increased the selective pressure and niche construction pace, as well as provided ‘micro-oxidation’ site on the electrode surface, thereby achieving the degradation of 4CP and mineralization of phenol. The porous electrodes could also adsorb contaminants and narrow their interaction distance with microbes, which benefited the degradation efficiency. Thus a 10-fold increase in the overall mineralization of DCP was achieved. This study constructed a novel bioelectrochemical system for achieving efficient and thorough biodechlorination, which was suitable for in situ bioremediation of groundwater.

New understanding of the main active substances and the promotion mechanism in the degradation of phenol by Fe–C micro-electrolysis systems

ABSTRACT The mechanism of phenol degradation by micro-electrolytic systems can be fully understood by evaluating the oxidation of active substances from the two aspects of phenol bond-breaking and mineralization, and the direction of promoting the generation of active substances is pointed out. In this article, the effects of H2O2, O2-•, ·OH and 1O2 in the degradation of phenol were analyzed using phenol and chemical oxygen demand (COD) removal rates as judgment indicators, respectively. And the addition of C6O8H6 to the micro-electrolysis system was adopted to promote the generation of active substances. The experimental results showed that the active substances which played a dominant effect in the process of phenol bond-breaking and mineralization were changed. While 1O2 is dominant in the bond-breaking of phenol, •OH is dominant in the mineralization of phenol. After adding C6O8H6 (1 mmol/L), the removal rates of phenol and COD were increased by 7.35 and 4.85%, respectively. This was attributed to the autoxidation reaction of C6O8H6 and the continuous supply of H+ while reducing Fe3+ to Fe2+. Additionally, the C6O8H6 regulated the reaction pathway to improve the utilization of H2O2. This study provides a new perspective for the understanding of active substances in micro-electrolysis systems.

Comparative study on CeO2 catalysts with different morphologies and exposed facets for catalytic ozonation: performance, key factor and mechanism insight

Morphology and facet effects of metal oxides in heterogeneous catalytic ozonation (HCO) are attracting increasing interests. In this paper, the different HCO performances for degradation and mineralization of phenol of seven ceria (CeO2) catalysts, including four with different morphologies (nanorod, nanocube, nanooctahedron and nanopolyhedron) and three with the same nanorod morphology but different exposed facets, are comparatively studied. CeO2 nanorods with (110) and (100) facets exposed show the best performance, much better than that of single ozonation, while CeO2 nanocubes and nanooctahedra show performances close to single ozonation. The underlying reason for their different HCO performances is revealed using various experimental and density functional theory (DFT) calculation results and the possible catalytic reaction mechanism is proposed. The oxygen vacancy (OV) is found to be pivotal for the HCO performance of the different CeO2 catalysts regardless of their morphology or exposed facet. A linear correlation is discerned between the rate of catalytic decomposition of dissolved ozone (O3) and the density of Frenkel-type OV. DFT calculations and in-situ spectroscopic studies ascertain that the existence of OV can boost O3 activation on both the hydroxyl (OH) and Ce sites of CeO2. Conversely, various facets without OV exhibit similar O3 adsorption energies. The OH group plays an important role in activating O3 to produce hydroxyl radical (∙OH) for improved mineralization. This work may offer valuable insights for designing Facet- and OV-regulated catalysts in HCO for the abatement of refractory organic pollutants.

Bubbleless membrane contactor for enhanced ozone mass transfer and ozonation for water purification

Membrane contactor, a physical barrier separating two phases to introduce gas into aqueous solutions through the bubbleless process, has gained considerable development for its improved gas transfer and contaminant removal efficiencies for water purification. However, a comprehensive assessment of a contactor with liquid flowing on the shell side and gaseous ozone flowing on the lumen side is scarce for ozonation. Therefore, we have developed a membrane contactor equipped with commercial hydrophobic polytetrafluoroethylene (PTFE) hollow fibers and investigated theoretically and experimentally the interaction between ozone and solution. Mass transfer behavior was evaluated by comparing experimental value and computational model of corresponding coefficients. Phenol was then selected as a model contaminant to evaluate the treatment performance of membrane contactors in ozonation. Crucial operating conditions involving the gas/liquid flow rate, concentrations of ozone and phenol, pH and geometry of fibers were assessed for their impacts on both ozone mass transfer and pollutant degradation. The results showed that the membrane presented high chemical resistance to ozone and could achieve stable mass transfer through bubbleless aeration. Under the optimum operating conditions, the overall liquid mass transfer coefficient was 1.12 × 10−5 m/s. The percentage removal and mineralization of phenol with 30 min hydraulic retention time could reach ∼100 % and 21.1 %, respectively, which have demonstrated the high treatment efficiency of the membrane contactor as an alternative technique in water purification.

Development of Highly Photoactive Mixed Metal Oxide (MMO) Based on the Thermal Decomposition of ZnAl-NO3-LDH

The highly crystalline ZnAl layered double hydroxides (ZnAl-NO3-LDHs) are utilized for the potential transformation into mixed metal oxides (MMOs) through thermal decomposition and used further for the photodegradation of phenol to assess the influence of calcination on ZnAl-LDHs with enhanced photoactivity. The structure, composition, and morphological evolution of ZnAl-LDHs to ZnO-based MMO nanocomposites, which are composed of ZnO and ZnAl2O4, after calcination at different temperatures (400–600 °C), are all thoroughly examined in this work. The final ZnO and ZnAl2O4-based nanocomposites showed enhanced photocatalytic activity. The findings demonstrated that calcining ZnAl-LDHs from 400 to 600 °C increased the specific surface area and also enhanced the interlayer spacing of d003 while the transformation of LDHs into ZnO/ZnAl2O4 nanocomposites through calcining the ZnAl-LDH precursor at 600 °C showed significant photocatalytic properties, leading to complete mineralization of phenol under UV irradiation.

Can xenobiotics support the growth of Mn(II)-oxidizing bacteria (MnOB)? A case of phenol-utilizing bacteria Pseudomonas sp. AN-1

Biogenic manganese oxides (BioMnOx) produced by Mn(II)-oxidizing bacteria (MnOB) have garnered considerable attention for their exceptional adsorption and oxidation capabilities. However, previous studies have predominantly focused on the role of BioMnOx, neglecting substantial investigation into MnOB themselves. Meanwhile, whether the xenobiotics could support the growth of MnOB as the sole carbon source remains uncertain. In this study, we isolated a strain termed Pseudomonas sp. AN-1, capable of utilizing phenol as the sole carbon source. The degradation of phenol took precedence over the accumulation of BioMnOx. In the presence of 100 mg L−1 phenol and 100 µM Mn(II), phenol was entirely degraded within 20 h, while Mn(II) was completely oxidized within 30 h. However, at the higher phenol concentration (500 mg L−1), phenol degradation reduced to 32% and Mn(II) oxidation did not appear to occur. TOC determination confirmed the ability of strain AN-1 to mineralize phenol. Based on the genomic and proteomics studies, the Mn(II) oxidation and phenol mineralization mechanism of strain AN-1 was further confirmed. Proteome analysis revealed down-regulation of proteins associated with Mn(II) oxidation, including MnxG and McoA, with increasing phenol concentration. Notably, this study observed for the first time that the expression of Mn(II) oxidation proteins is modulated by the concentration of carbon sources. This work provides new insight into the interaction between xenobiotics and MnOB, thus revealing the complexity of biogeochemical cycles of Mn and C.

Treatment of high-salt phenol wastewater by high-gravity technology intensified Co-Mn/γ-Al2O3 catalytic ozonation: Treatment efficiency, inhibition and catalytic mechanism

The treatment of high-salt phenol wastewater is still a challenging problem, and the effect of salt on the catalysts and active free radicals is still unclear. In this study, high-gravity technology intensified Co-Mn/γ-Al2O3 (CMA) catalytic ozonation is proposed for the treatment of high-salt phenol wastewater, and the effect of salt on catalysts and active free radicals is revealed. It is found that salt has little effect on the degradation of phenol in the high-gravity environment. The main reason for the poor mineralization of phenol is the accumulation of salt on the active sites of the catalyst rather than the scavenging of hydroxyl radicals (OH·). The CMA catalytic ozonation process follows OH· mechanism and was verified by electron paramagnetic resonance (EPR). Under the optimal conditions, the ηphenol reaches 98.40 % in 9 min and the ηTOC reaches 90.02 % in 80 min at a salt concentration of 10 g/L. Compared to the bubbling reactor (BR)/CMA/O3 (BCO) system, the ηphenol and ηTOC of the RPB/CMA/O3 (RCO) system are increased by 12.30 % and 15.90 %, respectively. This study not only provides a new method for the treatment of high-salt phenol wastewater, but also offers new insights into the effect of salt on active components.

The beneficial role of nano-sized Fe3O4 entrapped in ultra-stable Y zeolite for the complete mineralization of phenol by heterogeneous photo-Fenton under solar light

Highly efficient, separable, and stable magnetic iron-based-photocatalysts produced from ultra-stable Y (USY) zeolite were applied, for the first time, to the photo-Fenton removal of phenol under solar light. USY Zeolite with a Si/Al molar ratio of 385 was impregnated under vacuum with an aqueous solution of Fe2+ ions and thermally treated (500–750 °C) in a reducing atmosphere. Three catalysts, Fe-USY500°C-2h, Fe-USY600°C-2h and Fe-USY750°C-2h, containing different amounts of reduced iron species entrapped in the zeolitic matrix, were obtained. The catalysts were thoroughly characterized by absorption spectrometry, X-ray powder diffraction with synchrotron source, followed by Rietveld analysis, X-ray photoelectron spectroscopy, N2 adsorption/desorption at −196 °C, high-resolution transmission electron microscopy and magnetic measurements at room temperature.The catalytic activity was evaluated in a recirculating batch photoreactor irradiated by solar light with online analysis of evolved CO2. Photo-Fenton results showed that the catalyst obtained by thermal treatment at 500 °C for 2 h under a reducing atmosphere (FeUSY-500°C-2h) was able to completely mineralize phenol in 120 min of irradiation time at pH = 4 owing to the presence of a higher content of entrapped nano-sized magnetite particles. The latter promotes the generation of hydroxyl radicals in a more efficient way than the Fe-USY catalysts prepared at 600 and 750 °C because of the higher Fe3O4 content in ultra-stable Y zeolite treated at 500 °C. The FeUSY-500°C-2h catalyst was recovered from the treated water through magnetic separation and reused five times without any significant worsening of phenol mineralization performances. The characterization of the FeUSY-500°C-2h after the photo-Fenton process demonstrated that it was perfectly stable during the reaction. The optimized catalyst was also effective in the mineralization of phenol in tap water. Finally, a possible photo-Fenton mechanism for phenol mineralization was assessed based on experimental tests carried out in the presence of scavenger molecules, demonstrating that hydroxyl radicals play a major role.

A highly efficient supported TiO2 photocatalyst for wastewater remediation in continuous flow

Although TiO2 materials have been extensively studied as photocatalysts, there is not any commercial TiO2-supported photocatalyst used for wastewater remediation. This fact set the goal to synthesize a new supported titanium dioxide photocatalyst which, besides being robust, also has a high reaction surface and a very efficient TiO2 shell thickness. Hence, we present a novel TiO2-supported photocatalyst composed of titania-covered glass wool (GW) fibers decorated with SiO2@TiO2 core-shell spheres. For optimizing the photocatalytic activity of this material, the surface of SiO2 microspheres, as well as, the highly mechanically resistant GW fibers, were covered by a robust titania layer of ca. 20–30 nm of thickness. This layer contains nanometric crystals, ca. 12 nm in size, linked to each other and to the surfaces of both SiO2 microspheres and GW. An exhaustive characterization of the physicochemical properties of this new SiO2-TiO2 composite was performed to confirm the SiOTi linkage and the anatase crystal phase. The photocatalytic activity was initially evaluated in batch through the photodegradation of Methylene Blue as a standard dye. Afterward, the addition of the new photocatalyst in a solid phase stationary (SPS) photoreactor coupled to a TOC detector allowed studying in situ the mineralization of the recalcitrant pollutant phenol under a continuous flow regime. Results revealed that the optimized TiO2 surface of the SiO2-TiO2 composite produced the complete mineralization of phenol in less than three minutes. Even more, it was demonstrated that this photocatalyst is suitable for the industrial scale-up of wastewater treatment because it does not leach titania, its reuse does not require filtration procedures, and it can be easily implemented in SPS photoreactors at plant scale. In this context, the new material could be a good starting point to prepare other supported photocatalysts for wastewater remediation.

Efficient Microtubule Reactors for Mineralization of Phenol by Catalytic Ozonation Based on Macrokinetics

Efficient Microtubule Reactors for Mineralization of Phenol by Catalytic Ozonation Based on Macrokinetics

A green edge-hosted zinc single-site heterogeneous catalyst for superior Fenton-like activity

Developing green heterogeneous catalysts with excellent Fenton-like activity is critical for water remediation technologies. However, current catalysts often rely on toxic transitional metals, and their catalytic performance is far from satisfactory as alternatives of homogeneous Fenton-like catalysts. In this study, a green catalyst based on Zn single-atom was prepared in an ammonium atmosphere using ZIF-8 as a precursor. Multiple characterization analyses provided evidence that abundant intrinsic defects due to the edge sites were created, leading to the formation of a thermally stable edge-hosted Zn-N4 single-atom catalyst (ZnN4-Edge). Density functional theory calculations revealed that the edge sites equipped the single-atom Zn with a super catalytic performance, which not only promoted decomposition of peroxide molecule (HSO5-) but also greatly lowered the activation barrier for •OH generation. Consequently, the as-prepared ZnN4-Edge exhibited extremely high Fenton-like performance in oxidation and mineralization of phenol as a representative organic contaminant in a wide range of pH, realizing its quick detoxification. The atom-utilization efficiency of the ZnN4-Edge was ~104 higher than an equivalent amount of the control sample without edge sites (ZnN4), and the turnover frequency was ~103 times of the typical benchmark of homogeneous catalyst (Co2+). This study opens up a revolutionary way to rationally design and optimize heterogeneous catalysts to homogeneous catalytic performance for Fenton-like application.

Roles of alcohol group in functionalized carbon nitride for photocatalytic oxidation

Rational design of new active sites for g-C3N4-based photocatalysts to accelerate its charge transfer represents an advanced direction for pollutant photodegradation. Herein, alcohol group-modified g-C3N4 via integrated C-N site and –OH site using in situ C-N coupling is developed. The alcohol-modified g-C3N4 exhibits elevated phenol removal efficiency than g-C3N4. Experimental results and theoretic calculations disclosed that the C-N site adjacent to the introduced alcohol group not only constructs a built-in electric field for driving charge transfer but also acts as a new site for the activation of O2 molecules; the –OH site of alcohol group works as the adsorption site of phenol. Additionally, the discrepancy in activity between ethyl alcohol and methyl alcohol modification is due to the different oxidation ability, which is triggered by transfer rate of separated electrons. Importantly, this work achieved unique role of each active sites, providing a theoretical basis to the design of super-active photocatalysts, and reveals a clear pathway for evolution of ROS and phenol mineralization.

Photo‐Assisted Fenton Reaction for the Oxidative Degradation of Organic Pollutants in Water Using a Layered Double Hydroxide of Iron Ion

AbstractThe Fenton reaction is widely known as a promising method for treating organic pollutants. We investigated the photo‐assisted oxidative degradation of pollutants using various layered double hydroxides (LDHs) to develop heterogeneous Fenton catalyst capable of mineralizing organic pollutants. A LDH composed of Fe2+ and Al3+ (Fe2+Al3+‐LDH) under the irradiation of visible‐light (λ>420 nm) resulted in 2.5 times higher performance for the oxidative degradation (mineralization) of phenol as a model compound of organic pollutants compared with that without light irradiation. The ratio of Fe2+/Fe3+ on the surface of the Fe2+Al3+‐LDH after the reaction under the irradiation of visible‐light increased significantly compared with that without light irradiation. These indicated that the Fenton‐catalytic‐cycle was improved by reducing the Fe3+ generated after the Fenton reaction to the Fe2+ species by the photo‐assisted effects of the Fe2+Al3+‐LDH.

Precisely regulating hydroxyl groups and carbon vacancies on carbon nitride for in-situ photomineralization of phenol

Carbon vacancies Carbon nitride (CN) has been widely used in photomineralization of phenolic pollutants, during which avoiding the production of refractory polymers induced by hydroxyl radical (•OH) is the key. In CN photocatalytic system, O2 firstly reduces to superoxide radical (O2•-), then transforms into hydrogen peroxide (H2O2) via reduction and protonation process, finally reduces into •OH. In this study, OH/CV-CN, hydroxyl groups (–OH) and carbon vacancies (CV) co-modified CN, was designed for phenol photomineralization. –OH, not only act as the adsorption sites for phenol through O···H–O bond, but also assist introducing CV into CN during roasting process. CV, active sites for reducing O2 to O2•-, is close to adsorption sites of phenol, which greatly promotes the in-situ mineralization of phenol by O2•- and avoids the polymerization induced by •OH. Therefore, –OH and CV in OH/CV-CN synergistically facilitate the photomineralization of phenol.

Effect of CQDs doping on the properties of RuO2–TiO2/Ti anode

Phenol is a harmful substance that can cause pathological changes in animals or human body, and its degradation has become a research hotspot at present. This paper innovatively proposed the preparation of carbon quantum dots by microwave enhancement technology, the preparation of RuO2–TiO2-CQDs/Ti composite coating anode by thermal decomposition method, and studied the electrocatalytic degradation process of organic wastewater containing phenol. The surface morphology of the anode was observed by XPS, TEM and SEM. Electrochemical workstation was used to characterize the electrocatalytic performance of the anode, and high performance liquid chromatography was used to determine the degradation process. The results show that the doping of CQDs can produce a large number of vacancy defects on the surface of the composite coating, and the addition of CQDs can increase the loading of Ru element on the surface of the coating during anode preparation. With the increase of CQDs content, the crack width and depth of coating surface decrease gradually, and the crystal size decreases. Doping of CQDs can effectively improve the surface charge capacity and corrosion resistance of anode. Compared with the traditional RuO2–TiO2/Ti anode, the removal efficiency of phenol and COD at the RuO2–TiO2-CQDS/Ti composite coating electrode was increased by 102% and 55.7% respectively within 1 h. This study makes full use of the high specific surface area and excellent electrocatalytic performance of carbon quantum dots, which provides a new idea for the mineralization of high concentration phenol in Ru–Ti electrode.

Energy-oriented utilization from organic wastewater: Directional photoelectrocatalytic conversion of phenol to C1 fuels

To solve the problems of energy consumption, carbon emissions and pollution simultaneously, the directional conversion of phenol to hydrocarbon fuels through a pathway of “phenol → CO2 → HCO3–→HCOOH” was explored, with self-supplied CO2 as both carbon-based transition carrier and electron acceptor. In this economic approach, photoelectrocatalytic (PEC) deep mineralization of phenol was realized on the photoanode to provide CO2, together with the waste electrons from mineralization, was PEC converted into formate as the major liquid product on photocathode under an applied potential of 3 V and simulated sunlight. The total carbon utilization efficiency of phenol to hydrocarbons is 6.76%, and the conversion efficiency of formic acid is as high as 94.8% within 8 h PEC reaction. The integrated cell achieved the recovery of 2.75% waste electrons from phenol oxidation to produce liquid fuel. This work provides a promising “carbon neutral” strategy, which is important for realizing pollutant resource utilization and alleviating energy shortage.

Degradation of phenol with Mn-CoOX/γ-Al2O3 catalytic ozonation enhanced by high gravity technology

In this study, Mn-CoOX/γ-Al2O3 (MCA) was prepared by impregnation for catalytic ozonation of phenol in a rotating packed bed (RPB), and the effects of high gravity factor (β), liquid flow rate (QL), initial solution pH and gaseous ozone concentration (CO3) on the mineralization of phenol were explored. The results show that the degradation rate of phenol (ηphenol) reaches 100% at 9 min and the mineralization rate (ηTOC) reaches 95.01% at 45 min under conditions of β = 104, CO3= 80 mg L-1, QL = 80 L/h, and pH = 6. Compared with the bubbling reactor (BR)/MCA/O3 and O3/RPB systems, the ηTOC of the MCA/O3/RPB system is increased by 25.81% and 40.85%, respectively. The electron paramagnetic resonance (EPR) results reveal that hydroxyl radical (·OH) plays a critical role in the degradation of phenol by MCA catalyzed ozonation. The quenching experiment using tertiary butyl alcohol (TBA) as a scavenger of ·OH reveals that the ratio of direct and indirect degradation of phenol is 16:9. The intermediates generated during the degradation of phenol were detected by gas chromatography-mass spectrometry (GC–MS), and possible degradation pathways were proposed. In conclusion, MCA-catalyzed ozonation and RPB have a synergistic effect on ·OH initiation and improve the degradation and mineralization of phenol. This study provides a new perspective for the degradation of phenol.

Revealing the Role of Elementary Doping in Photocatalytic Phenol Mineralization

Photocatalytic mineralization of recalcitrant contaminants like phenol in wastewater requires abundant hydroxyl radicals (•OH) to initiate the reaction prior to the ring-opening. We here increase the free energy for adsorption of O* species on TiO2 surface and slightly downshift the band position by tin doping. This can simultaneously promote the generation and suppress the annihilation of •OH. Besides, tin doping can also facilitate semiconductor-cocatalyst-solution (SCS) interfacial electron transfer by lowering the potential barrier and synergistically enhance the photon utilization. By filming the photocatalyst onto our developed fixed bed reactors, the loss of photons resulting from undesirable absorption by contaminants can be alleviated. By these virtues, trace amount of phenol in wastewater can be efficiently mineralized.